Load driving device, illumination device, display device

ABSTRACT

A load driving device according to the present invention is provided with: an enabling control section generating an enabling signal from an externally inputted PWM signal; and a load driving section that is turned on/off according to the enabling signal, and that PWM-drives the load according to the PWM signal.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. Ser. No. 12/543,548, filedAug. 19, 2009, which in turn claims the benefit of Japanese ApplicationNo. 2008-211310, filed Aug. 20, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a load driving device capable ofachieving, by using a single external control signal, both on/offcontrol of the device itself and PWM (pulse width modulation) driving ofa load. For example, the present invention relates to an LED (lightemitting diode) driver IC supplying a drive current to an LED, and anillumination device and a display device using this.

2. Description of Related Art

FIG. 7 is a block diagram showing a conventional example of an LEDdriver IC. As shown in the figure, the conventional LED driver IC isconfigured such that an enabling signal EN for performing on/off controlof the LED driver IC is PWM-driven, to thereby PWM-drive a drive currentIo that is supplied to an LED from an LED driver section, and thus tocontrol the brightness of an LED (i.e., control a mean value of thedrive current Io).

In other words, the LED driver IC of this conventional example isconfigured such that an enabling signal EN for performing on/off controlof the LED driver IC itself and a brightness control signal PWM forcontrolling the brightness of an LED by PWM driving are combined into asingle external control signal.

An example of conventional technologies that the present inventionpertains is disclosed, for example, in JP-A-2008-61482 (hereinafter,Patent Document 1).

It is true that, with the above described conventional LED driver IC,since it is possible to achieve, by using a single external controlsignal, both on/off control of the LED driver IC itself and brightnesscontrol of the LED by PWM driving, the number of pins can be reduced.

However, with the above-described conventional LED driver IC, since itis configured such that the brightness control of the LED is performedby turning on/off the LED driver IC itself, internal circuits integratedon the LED driver IC are all started over from an off state each timethe enabling signal EN is raised from low to high level.

Thus, with the above-described conventional LED driver IC, between thetime when the enable signal EN is raised to high level and the time whenthe drive current Io supplied to the LED rises up to a desired currentvalue, there arises a time delay d (see FIG. 8) associated with start-upof a reference voltage supply, a reference current supply, and the likethat form the LED driver section (in particular, rising-up of areference voltage Vref).

This time delay d makes it impossible to obtain a drive current Iocorresponding to the on-duty (ratio of a high level period with respectto a cycle T in PWM driving) of the enabling signal EN. As a result,with the above-described conventional LED driver IC, as indicated by adash-dot line and a dash-dot-dot line in FIG. 9, a relation between theon-duty of the enabling signal EN and the drive current Io is moredeviated from an ideal one (see a solid line in FIG. 9) with increase infrequency f (=1/T) of PWM driving, and this invites degradation inlinearity, and reduction in dynamic range, of PWM driving.

Incidentally, the above problems can be solved with a configuration inwhich the enabling signal EN and the brightness control signal PWM areindependently inputted, but, inconveniently, such a configurationrequires an increased number of pins.

The above description deals with an LED driver IC as an example todescribe the problems that the present invention intends to overcome,but these problems are common to load driving devices in general thatachieve both on/off control of the devices themselves and PWM driving ofloads by using a single external control signal.

SUMMARY OF THE INVENTION

In view of the above problems, an object of the present invention is toprovide a load driving device capable of achieving, by using a singleexternal control signal, both on/off control of the device itself andPWM driving of a load without inviting degradation in linearity, orreduction in dynamic range, of PWM driving, and an illumination deviceand a display device using this.

To achieve the above object, according to one aspect of the presentinvention, a load driving device is provided with: an enabling controlsection generating an enabling signal from an externally inputted PWMsignal; and a load driving section that is turned on/off according tothe enabling signal and that PWM-drives the load according to the PWMsignal.

Other features, elements, steps, advantages and characteristics of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments thereof with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit block diagram showing a first embodiment of adisplay device according to the present invention;

FIG. 2A is a signal waveform diagram (showing a state in which an IC isbeing started up) for illustrating PWM operation of the firstembodiment;

FIG. 2B is a signal waveform diagram (showing a state in which the IC isbeing shut down) for illustrating PWM operation of the first embodiment;

FIG. 3 is a circuit block diagram showing a second embodiment of thedisplay device according to the present invention;

FIG. 4A is a signal waveform diagram (showing a state in which an IC isbeing started up) for illustrating PWM operation of the secondembodiment;

FIG. 4B is a signal waveform diagram (showing a state in which the IC isbeing shut down) for illustrating PWM operation of the secondembodiment;

FIG. 5 is a circuit block diagram showing a third embodiment of thedisplay device according to the present invention;

FIG. 6A is a signal waveform diagram (showing a state in which an IC isbeing started up) for illustrating PWM operation of the thirdembodiment;

FIG. 6B is a signal waveform diagram (showing a state in which the IC isbeing shut down) for illustrating PWM operation of the third embodiment;

FIG. 7 is a block diagram showing a conventional example of an LEDdriver IC;

FIG. 8 is a signal waveform diagram for illustrating conventional PWMoperation; and

FIG. 9 is a diagram showing a correlation between a PWM duty and a drivecurrent Io.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, a detailed description will be given, dealing with a casein which the present invention is applied to an LED driver IC.

First, a first embodiment of a display device according to the presentinvention will be described in detail with reference to FIG. 1. FIG. 1is a circuit block diagram showing the first embodiment of the displaydevice according to the present invention, and the figure shows the LEDdriver IC and vicinity thereof as a part particularly related to thepresent invention.

The display device of this embodiment is provided with an LED driver IC1, an LED 2 that receives a drive current Io from the LED driver IC 1and emits light, and a liquid crystal panel (not shown) that isilluminated by the LED 2 at its back or side surface.

The LED driver IC 1 is provided with: an enabling control section 10Athat generates an enabling signal EN from a brightness control signalPWM that is externally inputted thereto via a pin T1; and an LED driversection 20 that is turned on/off according to the enabling signal EN,and PWM-drives the LED 2 according to the brightness control signal PWM.Incidentally, the above-mentioned brightness control signal PWM is apulse signal subjected to pulse width modulation according to abrightness value of the LED 2.

In this embodiment, the enabling control section 10A is so configured asto generate a smooth voltage Vs from the brightness control signal PWMby using a smoothing circuit composed of a resistor 101 and d capacitor102, and pass this smooth voltage Vs through a buffer 103 so as togenerate the enabling signal EN. However, this is not meant to limit theconfiguration of the smoothing circuit, and a circuit configurationother than this may be adopted. In FIG. 1, a Schmitt buffer having ahysteresis property is used as the buffer 103, but instead, a bufferwithout a hysteresis property may be used, or, an inverter or acomparator may be used as the buffer 103.

Thus, the LED driver IC 1 is configured such that a single pin T1functions both as a brightness control terminal and as an enablingterminal, and furthermore, such that a signal path of the brightnesscontrol signal PWM and a signal path of the enabling signal EN areseparate from each other inside the IC.

The LED driver section 20 is provided with: a reference voltagegenerating circuit 201; P-channel MOS (metal oxide semiconductor)field-effect transistors 202 and 203; N-channel MOS field-effecttransistors 204 to 207; a resistor 208 (resistance: R); an operationalamplifier 209; and an inverter 210.

The reference voltage generating circuit 201 is means for generating apredetermined reference voltage Vref, and is allowed to generate, orprohibited from generating, the reference voltage Vref according to theenabling signal EN. More specifically, the reference voltage generatingcircuit 201 is in an operating state (state in which it is allowed togenerate the reference voltage Vref) when the enabling signal EN is highlevel, and the reference voltage generating circuit 201 is in anon-operating state (state in which it is prohibited from generating thereference voltage Vref) when the enabling signal EN is low level.

Sources of the transistors 202 and 203 are both connected to a powersupply terminal. Gates of the transistors 202 and 203 are both connectedto a drain of the transistor 202. The drain of the transistor 202 isconnected to a drain of the transistor 204. A source of the transistor204 is connected to a ground terminal via the resistor 208. Anon-inverting input terminal (+) of the operational amplifier 209 isconnected to a reference voltage Vref application terminal (i.e., anoutput terminal of the reference voltage generating circuit 201). Aninverting input terminal (−) of the operational amplifier 209 isconnected to the source of the transistor 204. An output terminal of theoperational amplifier 209 is connected to a gate of the transistor 204.A drain of the transistor 203 is connected to drains of the transistors205 and 206. Gates of the transistors 206 and 207 are connected to thedrain of the transistor 206. Sources of the transistors 205 to 207 areconnected to the ground terminal. A drain of the transistor 207 isconnected to a cathode of the LED 2 via a pin T2. An input terminal ofthe inverter 210 is connected to a brightness control signal PWMapplication terminal (i.e., the pin T1). An output terminal of theinverter 210 is connected to a gate of the transistor 205.

Incidentally, in the above-structured LED driver section 20, thetransistor 204, the resistor 208, and the operational amplifier 209 forma V/I conversion circuit that converts the reference voltage Vref into areference current Ia (=Vfef/R). The transistors 202 and 203 form a firstcurrent mirror circuit that generates a mirror current Ib (=m×Ia) fromthe reference current Ia. The transistors 206 and 207 form a secondcurrent mirror circuit that generates a drive current To (=n×Ib=m×n×Ia)for the LED 2 from the mirror current Ib. The transistor 205 and theinverter 210 form a switch circuit that, based on the brightness controlsignal PWM, allows or prohibits operation of the second current mirrorcircuit. More specifically, when the brightness control signal PWM ishigh level, the transistor 205 is in an off state and the second currentmirror circuit is in an operating state (state in which the secondcurrent mirror circuit is allowed to generate the drive current Io), andwhen the brightness control signal PWM is low level, the transistor 205is in an on state, and the second current mirror circuit is in anon-operating state (state in which the second current mirror circuit isprohibited from generating the drive current Io).

That is, in the above-structured LED driver section 20, the transistors202 to 207, the resistor 208, the operational amplifier 209, and theinverter 210 form a drive current generating circuit that generates thedrive current To for the LED 2 by converting the reference voltage Vrefinto a current, and this drive current generating section is allowed togenerate, or prohibited from generating, the drive current To accordingto the brightness control signal PWM.

Next, PWM operation performed by the above-structured LED driver IC 1will be described in detail, with reference to the signal waveformdiagrams of FIGS. 2A and 2B. FIGS. 2A and 2B are signal waveformdiagrams for illustrating the PWM operation of the first embodiment.FIG. 2A shows a state in which the IC is being started up, and FIG. 2Bshows a state in which the IC is being shut down. In each figure aredescribed the brightness control signal PWM, the smooth voltage Vs, theenabling signal EN, the reference voltage Vref, and the drive currentIo, in this order from top to bottom.

First, starting operation of the IC will be described with reference toFIG. 2A. When, at time t11, the brightness control signal PWM starts tobe inputted so that its voltage level is raised from low to high level,the smooth voltage Vs obtained by smoothing the brightness controlsignal PWM starts to rise, and when its voltage level exceeds athreshold level of the buffer 103, the enabling signal EN rises from lowto high level. Incidentally, it is preferable that the threshold levelof the buffer 103 be properly so set as to allow the enabling signal ENto continuously maintain itself at high level while the brightnesscontrol signal PWM is being inputted.

The reference voltage generating circuit 201 enters an operating statein response to the above-described shift of the enable signal EN to highlevel, and starts generating the reference voltage Vref. The referencevoltage Vref, taking a predetermined rise-up time, rises up to a targetvoltage level, and thereafter, it is maintained at the voltage level.The drive current Io is PWM-driven according to the brightness controlsignal PWM, and thus brightness control of the LED 2 (mean value controlof the drive current Io) is performed.

Next, shutdown operation of the IC will be described with reference toFIG. 2B. When, after the input of the brightness control signal PWM isfinished at time t13, the voltage level of the brightness control signalPWM is maintained at low level, the smooth voltage Vs obtained bysmoothing the brightness control signal PWM falls, and at a time whenthe voltage level of the smooth voltage Vs falls below the thresholdlevel of the buffer 103, the enabling signal EN falls from high to lowlevel. On the other hand, the reference voltage generating circuit 201,in response to the above-mentioned level shift of the enabling signal ENto low level, enters a non-operating state, and thus stops generatingthe reference voltage Vref.

As described above, the LED driver IC 1 of this embodiment generates,from the brightness control signal PWM externally inputted via the pinT1, the enabling signal EN that is transmitted, inside the IC, along asignal path different from a signal path along which the brightnesscontrol signal PWM is transmitted. The LED driver IC 1 performs its ownon/off control (in the example of FIG. 1, generation control of thereference voltage Vref) by using the thus generated enabling signal EN,and it also controls the brightness of the LED 2 by using the PWM-drivenbrightness control signal PWM.

With this configuration, while the brightness control signal PWM isbeing inputted, the enabling signal EN can be maintained at high leveland the drive current Io can be PWM-driven with the LED driver IC 1itself maintained in an on state. Thus, the LED driver IC 1 itself doesnot need to be repeatedly turned on/off to control the brightness of theLED 2.

Thus, although there arises a time delay associated with the start-up ofthe LED driver IC 1 (in particular, the rising-up of the referencevoltage Vref) when the LED driver IC 1 is started up for the first timeat time t11, from time t2 onward, the drive current Io can be PWM-drivenin a state in which the start-up of the LED driver IC 1 is complete,only an extremely short delay arises at the rising-up of the drivecurrent Io, and this makes it possible to obtain the drive current Iocorresponding to the on-duty of the brightness control signal PWM.Incidentally, in view of the fact that the brightness of the LED 2 iscontinuously carried out from time t12 onward, the rising-up delay ofthe drive current Io arising only at the first start-up hardly has anyeffect on the overall brightness control, and thus no particular problemseems to be cause by neglecting it.

Thus, with the LED driver IC 1 of this embodiment, both on/off controlof the LED driver IC 1 itself and PWM driving of the LED 2 can beachieved by using a single external control signal (in FIG. 1, thebrightness control signal PWM) without inviting degradation inlinearity, or reduction in dynamic range, of the PWM driving. Inparticular, the present invention can be said to be extremely effectivein increasing the frequency f (=1/T) of the PWM driving.

Next, a second embodiment of the display device according to the presentinvention will be described in detail with reference to FIG. 3. FIG. 3is a circuit block diagram showing the second embodiment of the displaydevice according to the present invention, and the figure shows the LEDdriver IC and vicinity thereof as a part particularly related to thepresent invention.

As shown in FIG. 3, the LED driver IC 1 of this embodiment, which hassubstantially the same configuration as that of the first embodiment, isfeatured in that, instead of the enabling control section 10A using asmoothing circuit, an enabling control section 10B using a latch circuitis incorporate therein, and in that it is further provided with a resetcontrol section 30. Thus, the same components as those in the firstembodiment are identified by the same reference numerals as in FIG. 1,thereby omitting an overlapping description, and the description belowwill be concentrated on the features of this embodiment.

In the LED driver IC 1 of this embodiment, the enabling control section10B is a latch circuit that is triggered by a rising edge of thebrightness control signal PWM to set the enabling signal EN to highlevel, and that is triggered by a rising edge of a reset signal RST toreset the enabling signal EN to low level. For example, in a case inwhich a D flip-flop is used as the enabling control section 10B, a dataterminal (D) is connected to a high-level signal application terminal(for example, the power supply terminal), a clock terminal is connectedto the pin T1, a reset terminal is connected to a reset signal RSTapplication terminal (that is, an output terminal of the reset controlsection 30), and an output terminal (Q) is connected to an enablingsignal input terminal of the LED driver section 20.

The reset control section 30 is means that counts time for which thebrightness control signal PWM is maintained at low level, and that, whena value of the time counted thereby reaches a predetermined value,generates the reset signal RST so as to reset the enabling controlsignal EN. As means for counting the just-mentioned time, a counter thatcounts a predetermined internal clock signal is used.

Next, a detailed description will be given of PWM operation by the LEDdriver IC 1 configured as described above with reference to the signalwaveform diagrams of FIGS. 4A and 4B. FIGS. 4A and 4B are signalwaveform diagrams for illustrating the PWM operation of the secondembodiment. FIG. 4A shows a state in which the IC is being started up,and FIG. 4B shows a state in which the IC is being shut down. In eachfigure are described the brightness control signal PWM, the reset signalRST, the enabling signal EN, the reference voltage Vref, and the drivecurrent Io, in this order from top to bottom.

First, start-up operation of the IC will be described with reference toFIG. 4A. When, at time t21, the brightness control signal PWM starts tobe inputted so that its voltage level is raised from low to high, theenabling signal EN is triggered by the rising edge to be set to highlevel from low level.

The reference voltage generating circuit 201 (not shown in FIG. 3) thatforms the LED driver section 20 enters an operating state in response tothe above-described shift of the enabling signal EN to high level, andstarts generating the reference voltage Vref. The reference voltageVref, taking a predetermined rise-up time, rises up to a target voltagelevel, and is maintained at the voltage level thereafter. The drivecurrent Io is PWM-driven according to the brightness control signal PWM,and thus brightness control of the LED 2 (mean value control of thedrive current Io) is performed.

Next, shutdown operation of the IC will be described with reference toFIG. 4B. When, after the input of the brightness control signal PWM isfinished at time t23, the voltage level of the brightness control signalPWM has been maintained at low level for a predetermined time Toff, thereset signal RST is raised to high level, and thereby the enablingsignal EN is triggered to be reset to low level from high level. On theother hand, the reference voltage generating circuit 201 that forms theLED driver section 20, in response to the above-mentioned level shift ofthe enabling signal EN to low level, enters a non-operating state, andstops generating the reference voltage Vref.

As depicted above, with the LED driver IC of this embodiment, as withthat of the first embodiment, while the brightness control signal PWM isbeing inputted, the enabling signal EN can be maintained at high leveland the drive current Io can be PWM-driven, with the LED driver IC 1itself maintained in an on state. Thus, the LED driver IC 1 itself doesnot need to be repeatedly turned on/off to control the brightness of theLED 2. This makes it possible to achieve, by using a single externalcontrol signal, both the on/off control of the LED driver IC 1 itselfand the PWM driving of the LED 2 without inviting degradation inlinearity, or reduction in dynamic range, of the PWM driving.

Next, a third embodiment of the display device according to the presentinvention will be described in detail with reference to FIG. 5. FIG. 5is a circuit block diagram showing the third embodiment of the displaydevice according to the present invention, and the figure shows the LEDdriver IC and vicinity thereof as a part particularly related to thepresent invention.

As shown in FIG. 5, the LED driver IC 1 of this embodiment hassubstantially the same configuration as that of the second embodiment,and it is featured in that a masking control section 40 is furtherprovided. Thus the same components as those in the second embodiment areidentified by the same reference numerals as in FIG. 3, thereby omittingan overlapping description, and the description below will beconcentrated on the features of this embodiment.

In the LED driver IC 1 of this embodiment, the masking control section40, which is means for prohibiting supply of the brightness controlsignal PWM to the LED driver section 20 until a predetermined maskingtime Tm has elapsed after a start of an external input of the brightnesscontrol signal PWM, is provided with a counter 41 and an AND operationunit 42. The counter 41 is means for counting a number of pulses in thebrightness control signal PWM and shifting a masking signal MSK from lowlevel to high level when the counted value reaches a predeterminedvalue. The AND operation unit 42 is means for performing an ANDoperation between the brightness control signal PWM and the maskingsignal MSK and supplying the operation result to the LED driver section20 as a masked brightness control signal PWM′.

Next, a detailed description will be given of PWM operation by the LEDdriver IC 1 configured as described above with reference to the signalwaveform diagrams of FIGS. 6A and 6B. FIGS. 6A and 6B are signalwaveform diagrams for illustrating the PWM operation of the thirdembodiment. FIG. 6A shows a state in which the IC is being started up,and FIG. 6B shows a state in which the IC is being shut down. In eachfigure are described the brightness control signal PWM, the reset signalRST, the enable signal EN, the masking signal MSK, the masked brightnesscontrol signal PWM′, the reference voltage Vref, and the driving currentIo, in this order from top to bottom. Incidentally, FIG. 6A shows, as anexample, a case in which time taken for the reference voltage Vref torise up is longer than a cycle T of the PWM driving, and the maskingsignal MSK is raised to high level with a fourth pulse in the brightnesscontrol signal PWM.

First, the start-up operation of the IC will be described with referenceto FIG. 6A. When, at time t31, the brightness control signal PWM startsto be inputted so that its voltage level is raised from low to highlevel, the enabling signal EN is triggered by the rising edge to be setto high level from low level. The reference voltage generating circuit201 (not shown in FIG. 5) that forms the LED driver section 20 enters anoperating state in response to the above-described shift of the enablingsignal EN to high level, and starts generating the reference voltageVref. The reference voltage Vref, taking a predetermined rise-up time,rises up to a target voltage level, and is maintained at the voltagelevel thereafter.

At time t31, the counter 41 counts the number of pulses in thebrightness control signal PWM, and “1” is stored as a count value.Thereafter, each time a pulse is raised in the brightness control signalPWM, at time t32 and time t33, the count value is incremented to “2” and“3”, respectively. Here, until the count value reaches “4”, since themasking signal MSK is maintained at low level, the masked brightnesscontrol signal PWM′ is maintained at low level regardless of the logiclevel of the externally inputted brightness control signal PWM, and thusthe generation of the drive current Io at the LED driver section 20 isstopped.

Then, when, at time t34, a fourth pulse is raised in the brightnesscontrol signal PWM and the count value counted by the counter 41 reaches“4”, the masking signal MSK is set from low level to high level, under ajudgment that the predetermined masking time Tm has elapsed since thestart of the external input of the brightness control signal PWM. As aresult, the logic level of the masked brightness control signal PWM′becomes equal to that of the externally inputted brightness controlsignal PWM, the drive current Io starts to be PWM-driven at the LEDdriver section 20, and thus brightness control of the LED 2 (mean valuecontrol of the drive current Io) is performed.

Next, shutdown operation of the IC will be described with reference toFIG. 6B. When, after the input of the brightness control signal PWM isfinished at time t35, the voltage level of the brightness control signalPWM has been maintained at low level for a predetermined time Toff, thereset signal RST is raised to high level, and thereby the enablingsignal EN is triggered to be reset to low level from high level. On theother hand, the reference voltage generating circuit 201 that forms theLED driver section 20, in response to the above-mentioned level shift ofthe enabling signal EN to low level, enters a non-operating state, andstops generating the reference voltage Vref.

As described above, with the LED driver IC 1 of this embodiment, sinceunstable generation of the drive current To can be prohibited in thetransition period when the reference voltage Vref has not reached atarget voltage level, it is possible to achieve a more stable PWMdriving of the LED2 (see the parts indicated by broken lines in FIG.6A).

Incidentally, although the above description deals with, as an example,a configuration obtained by additionally providing the masking controlsection 40 to the configuration of the second embodiment, this is notmeant to limit the configuration of the present invention, and theconfiguration of the first embodiment may be additionally provided withthe masking control section 40.

Also, although the above description deals with a configuration whichuses the AND operation unit 42 as means for connecting/disconnecting thesignal path of the brightness control signal PWM, this is not meant tolimit the configuration of the present invention, and an analog switchor the like may be used.

Also, although the above description deals with a configuration in whichthe counter 41 counts the number of pulses in the brightness controlsignal PWM, this is not meant to limit the configuration of the presentinvention, and, like in the reset control section 30, the counter 41 maycount a separate internal clock signal.

Also, although the above-described first to third embodiments deal withconfigurations in which the present invention is applied to an LEDdriver IC, this is not meant to limit the application target of thepresent invention, and the present invention can be widely applied toload driving devices in general achieving both on/off control of thedevices themselves and PWM driving of loads by using a single externalcontrol signal.

It should be understood that, other than the first to third embodimentsdescribed above, many modifications and variations are possible withinthe spirit of the present invention.

As hitherto described, according to the technology disclosed in thisspecification, it is possible to provide a load driving device capableof achieving, by using a single external control signal, both on/offcontrol of the device itself and PWM driving of a load without invitingdegradation in linearity, or reduction in dynamic range, of the PWMdriving, and an illumination device and a display device using this.

The technology disclosed in this specification can be preferablyapplied, for example, to an LED driver IC supplying a drive current toan LED, and an illumination device and a display device using this.

While the present invention has been described with respect to preferredembodiments, it will be apparent to those skilled in the art that thedisclosed invention may be modified in numerous ways and may assume manyembodiments other than those specifically set out and described above.Accordingly, it is intended by the appended claims to cover allmodifications of the present invention which fall within the true spiritand scope of the invention.

What is claimed is:
 1. A load driving device, comprising: an enablingcontrol section generating an enabling signal from an externallyinputted PWM signal; and a load driving section that is turned on/offaccording to the enabling signal, and that also PWM-drives the loadaccording to the PWM signal, wherein the load driving section includes:a reference voltage generating circuit generating a predeterminedreference voltage; and a drive current generating circuit generating adrive current for the load by converting the reference voltage into acurrent, wherein the reference voltage generating circuit is allowed togenerate, or prohibited from generating, the reference voltage accordingto the enabling signal, wherein the drive current generating circuit isallowed to generate, or prohibited from generating, the drive currentaccording to the PWM signal, and wherein the enabling control section isa delay circuit generating the enabling signal by delaying the PWMsignal.
 2. The load driving device of claim 1, wherein the delay circuitincludes a lowpass filter.
 3. The load driving device of claim 2,wherein the low-pass filter is a CR time constant circuit.
 4. The loaddriving device of claim 3, wherein the delay circuit includes a bufferconnected to a latter stage of the low-pass filter.
 5. The load drivingdevice of claim 1, further comprising: a masking control section thatprohibits the PWM signal from being supplied to the load driving sectionfor a predetermined time after a start of external input of the PWMsignal.
 6. The load driving device of claim 1, wherein, as the load, alight emitting device is connected to the load driving device.
 7. Anillumination device, comprising: a light emitting device serving as alight source; and a load driving device supplying a drive current to thelight emitting device, wherein the load driving device includes: anenabling control section generating an enabling signal from anexternally inputted PWM signal; and a load driving section that isturned on/off according to the enabling signal, and that also PWM-drivesthe light emitting device according to the PWM signal, wherein the loaddriving section comprises: a reference voltage generating circuitgenerating a predetermined reference voltage; and a drive currentgenerating circuit generating a drive current for the load by convertingthe reference voltage into a current, wherein the reference voltagegenerating circuit is allowed to generate, or prohibited fromgenerating, the reference voltage according to the enabling signal,wherein the drive current generating circuit is allowed to generate, orprohibited from generating, the drive current according to the PWMsignal, and wherein the enabling control section is a delay circuitgenerating the enabling signal by delaying the PWM signal.
 8. Theillumination device of claim 7, wherein the delay circuit includes alowpass filter.
 9. The illumination device of claim 8, wherein thelow-pass filter is a CR time constant circuit.
 10. The illuminationdevice of claim 9, wherein the delay circuit includes a buffer connectedto a latter stage of the low-pass filter.
 11. The illumination device ofclaim 7, wherein the load driving device further comprises: a maskingcontrol section that prohibits the PWM signal from being supplied to theload driving section for a predetermined time after a start of externalinput of the PWM signal.
 12. A display device, comprising: a liquidcrystal panel; and an illumination device illuminating the liquidcrystal panel, wherein the illumination device comprises: a lightemitting device serving as a light source; and a load driving devicesupplying a drive current to the light emitting device, wherein the loaddriving device comprises: an enabling control section generating anenabling signal from an externally inputted PWM signal; and a loaddriving section that is turned on/off according to the enabling signal,and that also PWM-drives the light emitting device according to the PWMsignal, wherein the load driving section includes: a reference voltagegenerating circuit generating a predetermined reference voltage; and adrive current generating circuit generating a drive current for the loadby converting the reference voltage into a current, wherein thereference voltage generating circuit is allowed to generate, orprohibited from generating, the reference voltage according to theenabling signal, wherein the drive current generating circuit is allowedto generate, or prohibited from generating, the drive current accordingto the PWM signal, and wherein the enabling control section is a delaycircuit generating the enabling signal by delaying the PWM signal. 13.The display device of claim 12, wherein the delay circuit includes alow-pass filter.
 14. The display device of claim 13, wherein thelow-pass filter is a CR time constant circuit.
 15. The display device ofclaim 4, wherein the delay circuit includes a buffer connected to alatter stage of the low-pass filter.
 16. The illumination device ofclaim 12, wherein the load driving device further comprises: a maskingcontrol section that prohibits the PWM signal from being supplied to theload driving section for a predetermined time after a start of externalinput of the PWM signal.